The nerve agent used to poison Russian opposition leader Alexei Navalny was detected on an empty water bottle from his hotel room in the Siberian city of Tomsk, suggesting he was poisoned there and not at the airport as first thought, his team said on Thursday.

Navalny fell violently ill on a flight in Russia last month and was airlifted to Berlin for treatment. Laboratories in Germany, France and Sweden have established he was poisoned by a Novichok nerve agent, a poison developed by the Soviet military, though Russia denies this and says it has seen no evidence.